1. Field of The Invention
The present invention relates to a technology of processing and observing a sample by charged particle beams, and for example to a charged particle beam apparatus to produce a processed surface on a fine sample extracted from a substrate of a semiconductor device by applying microprocessing to a specific portion by FIBs (Focused Ion Beam) and observe the processed surface with a scanning transmission electron microscope (STEM), a transmission electron microscope (TEM), a scanning electron microscope (SEM), or the like.
2. Description of the Related Art
A technology on the combination of an FIB apparatus and an STEM apparatus is disclosed in Japanese Patent Laid-Open No. 2004-228076. It shows that an STEM observation sample produced by FIB processing is placed at the intersection of an ion beam axis and an electron beam axis and can be subjected to additional FIB processing and STEM observation. The ion beam axis and the electron beam axis intersect at acute angles (about 45 degrees in the case shown FIG. 5) and the STEM sample is rotated around a rotation shaft perpendicular to both the axes during the time between the additional FIB processing and the STEM observation.
Further, Japanese Patent Laid-open No. 2006-127850 describes a technology of realizing: the omission and minimization of the sample rotation or the like during the time between the FIB processing and the STEM observation; and the simplification in the operation of optimizing a sample thickness with an STEM image monitor during processing. According to the technology, an ion beam system, an electron beam system, and a transmitted and scattered beam detection device are disposed around a sample, the illumination axis of the FIB system and the illumination axis of the electron beam system for STEM observation are arranged so as to form nearly right angles to each other, and the sample is placed at the intersection. By so doing, it is possible to carry out both the FIB processing and the STEM observation without the sample displaced.
THE TRC NEWS No. 84, July, 2003 (Kato and Otsuka, Toray Research Center, Inc.) describes a means of three-dimensional structural analysis by FIB processing and SEM observation. Both the illumination axes of the FIB system and the electron beam system intersect with each other at acute angles and it is possible to display an image in the same region with the scanned images of both the beams, namely with the scanning ion microscopic image (the SIM image) and the SEM image. As it is anticipated from the electron beam system, by processing across section by FIBs, it is possible to observe the processed cross section with an SEM without the sample inclined. By repeating the FIB processing and the SEM observation, it is possible to integrate continuous segmented images in the direction of the depth from the processed surface.
The FIB processing and the STEM observation have heretofore been carried out with separate apparatuses in many cases. A thin film sample for an STEM processed with an FIB apparatus had to be once extracted from the FIB apparatus, and thereafter observed with an STEM apparatus. Thin film processing wherein an observed portion was identified by repeating the STEM observation and the additional FIB processing could not meet users' needs sufficiently from the viewpoint of throughput. To cope with the problem, an apparatus integrating FIB processing and STEM observation is announced and the improvement of throughput is attempted.
However, in such a case as to process a sample the exact defective portion and the defect size of which are not known into a thin film while an intended defective portion is retained, drastic improvement in throughput has not been attained yet because of the reasons: (1) a thin film sample larger than an ordinary sample is produced; (2) the repetition of FIB processing and SEM or STEM observation by cross section monitoring is carried out more frequently than usual and thin film processing is carried out while the observation portion is judged; (3) the region of processing itself expands; and others.
The fact that a cross section cannot be observed with an SEM or an STEM during FIB processing is one of the factors that cause throughput to be prevented from improving. Further, in the case of a sample having plural cross sections such as a thin film sample, when the plural cross sections are observed with an SEM or an STEM, displacement operation such as rotation and inclination of the sample or a sample stage is necessary in order to irradiate the cross section to be observed with electron beams. Furthermore, once a sample is displaced, visual field readjustment and focus readjustment are required. From those factors, even an apparatus integrating FIB processing and STEM observation can hardly secure a sufficient throughput.
In the case of three-dimensional structural analysis by FIB processing and SEM observation too, there are similar problems since the FIB processing and the SEM observation are repeated alternately. When the three-dimensional structural analysis is applied to a large region, visual field deviation and focus deviation appear in an SEM observed cross-sectional image as the FIB processing advances, hence it is necessary to adjust the visual field and the focus of the SEM frequently, and such operation is a factor causing the throughput to deteriorate.
Further in recent years, in order to realize a microstructure having high electrical characteristics, a material called a Low-K material that is very susceptible to electron beam irradiation has come to be used much and the cases of destroying or deforming a sample by electron beam irradiation during SEM observation and the like have come to happen frequently. The Low-K material is a low permittivity materials made of, for example, organic polymer or SiOC etc. As measures against the cases, means such as (1) to mitigate damage by cooling a sample, (2) to extremely lower the acceleration voltage of electron beams and reduce irradiation energy, and others have been taken.
However, the means (1) requires time for cooling and exchanging samples and the throughput of processing lowers enormously. Further, the damage caused by electron beam irradiation appears locally and the observed portion deforms even though the sample stage is cooled unless a cooling path is sufficiently secured. A drawback of the means (2) is that the image resolution of an SEM lowers by lowering the acceleration voltage of electron beams and the microstructure is hardly recognized.